1. Field of the Invention
The present invention relates to a polishing device and a polishing method. More particularly, the present invention relates to a polishing device and polishing method for flattening a wafer surface using a CMP (Chemical Mechanical Polishing) process.
2. Description of the Related Art
Conventionally, a process for flattening a wafer surface after predetermined film formation is essential in the manufacture of a semiconductor device. The reason is that when asperities occur on a wafer surface, the following problems may occur. That is, a coating property of a subsequently formed film deteriorates and therefore, breaking of wire or insulation failure is caused, or a coating film thickness of resist changes in a lithography step or a lens is put into an unfocused condition during exposure and therefore, it becomes difficult to form a micropattern. At present, the CMP process for performing polishing by pressing a wafer against a surface of a polishing pad and rotating the wafer and the pad while supplying a working fluid containing abrasive grains is widely used in the flatness of a wafer surface.
For the CMP process, for example, the following methods are heretofore proposed. One method is such that in order to suppress a scratch which may occur in rubbing both surfaces of a wafer and a polishing pad to perform the polishing as described above, a polishing pad which contains impurities in a concentration of a fixed value or less and which is harder than the wafer is used or a needle-shaped abrasive grain is used (see, e.g., Japanese Unexamined Patent Application Publication No. 2000-49122). Another method is such that using a polyvinyl-chloride brush with a predetermined shape in place of an ordinary polishing pad, polishing of a wafer surface is performed by rotating the brush while supplying a working fluid and then, water or drug solution is supplied to the wafer surface after the polishing to clean the surface using the brush, if necessary (see, e.g., Japanese Unexamined Patent Application Publication No. 2003-109919).
However, a conventionally used polishing pad is formed of a material having elasticity, such as urethane. In a case of using such a polishing pad in polishing of a wafer, when the wafer is pressed against the polishing pad, the polishing pad follows asperities on a wafer surface. As a result, steps remain on the wafer surface even after the polishing so that the wafer surface may fail to obtain sufficient flatness.
FIG. 15 illustrates a conventional polishing method.
When a surface of a wafer 100 as shown in FIG. 15 is polished using a polishing pad 101 having elasticity, a working fluid containing abrasive grains 102 is flowed between the wafer 100 and the polishing pad 101 as well as the wafer 100 is pressed against the polishing pad 101. On this occasion, each of the wafer 100 and the pad 101 is rotated.
At this time, assume that the wafer 100 has a structure that on a surface of an insulating film 103a having formed thereon wirings 104a and 104b, an insulating film 103b is further deposited. In this case, asperities of the insulating film 103b in response to pattern shapes of the wirings 104a and 104b are formed on the wafer 100 surface. When the wafer 100 with such a surface shape is pressed against the polishing pad 101, the polishing pad 101 follows the asperities on the wafer 100 surface for the sake of the elasticity thereof. Therefore, during the polishing, the convex portions on the wafer 100 surface are polished as well as the concave portions thereon are polished. As a result, steps remain on the wafer 100 surface even after the polishing.
FIGS. 16 and 17 show examples of wafer shapes after polishing.
When the polishing pad follows asperities as described above, the following problems occur. For example, when a wiring 201a, and wirings 201b and 201c are present at a certain distance within a wafer 200 as shown in FIG. 16, dishings may occur therebetween. Further, when the wafer 300 has in the inside thereof an area where wirings 301a, 301b, 301c, 301d, 301e and 301f are thickly present as shown in FIG. 17, global steps may occur on each side of the area.
Further, in the polishing of a wafer surface using a polishing pad, the polishing pad and the wafer are rotated and the surfaces thereof are rubbed. Therefore, when relatively large foreign objects (abrasive grains contained in a working fluid or residues produced by polishing) are mixed between the polishing pad and the wafer during the polishing, a large scratch, that is, a scratch extending over a number of chip areas on the wafer easily occurs.
By changing the polishing pad into a harder one, the dishings or the global steps can be somewhat reduced in occurrence. However, even in the case of thus changing the polishing pad into the harder one, it is difficult to prevent the scratch from occurring as long as the polishing is performed by rubbing the surfaces. On the contrary, a widespread scratch may occur deeply by changing the polishing pad into the harder one.